Method of making spark plugs



Febf24, 1942. H. RABEzzANA METHOD OF-MAKING SPARK PLUGS Filed Feb. 24;1941 2 Sheets-Sheet l attorneys Feb. 24, 1942. H. RABEzzANA METHOD OFMAKING SPARK PLUGS Filed Feb. 24, 1941 2 Sheets-Sheet 2 :inventorPatented Feb. 24, 41942 v Mncrnon or mmc SPARK PLUGS Hector Rabemna,Flint', Mich., assigner to General Motors Corporation, Detroit, Mich., aoorporation of Delaware Figure 1.as having been '5' ApplicationFebruarylza 1941, serial No. 380,215

s claims '(cl. zal-155.51)

My invention relates to spark plugs wherein the insulating member isheld in place within tlie shell or casing by a securing member having yl ying lapparatus in side elevation, usable for weldlarge openingsin itsperipheral wall, whereby the.

surrounding atmosphere hasfree access' tothe outer part of theinsulating member and better cooling of the plug'is secured; and thesame con'- sists in an improved method of making aholding 'member forsecuring the insulating member of a spark plug assembled with the otherele- ,ments thereof; said insulator vsecuring member being made fromhexagonal bar stock by performing certain milling, boring, cutting-offand equivalent operations upon said bar; whereby features ofconstruction of said insulator securing member hereinafter enumeratedare provided. My' invention consists, further, in the f method of makinga complete spark plug by assembling a. securing member made ashereinafter explained with a suitable insulating .mem-

screw into a threaded opening in an internal .combustion enginecylinder; Vand in welding the extremities of certain spaced lugs of saidsecuring member, produced inA the manufacture thereof, to the free upperor outer end of said shell.

Referring now to the drawings for a more comt plete understanding of themethodl whereinmy invention consists:

Figure 1 is a view showing ahexagonal bar used in making insulatorsecuring members for spark plugs in accordance with my invention.

Figure 2 is a view showing the bar shown in provided with a lgroove ineach of its six faces.

" Figure 3 is a' view showiiigian insulatorsecur- .ing member formedupon the end of said hanr but not cut @if therefrom. y

'Figure 4 is .a fragmentary. sectional/.view i l luistrating myinvention.

Figure 5 `is a vieil;1 showing a section uponv aN central planeextending longitudinally-thereof. of a spark plug made'in accordancewith my in ber, suitable gaskets, and a shell designed toV .down from atransverse plane indicated broken line lll-lll, Figure 9.

ing the extremities of depending lugs ofthe insulator securing member tothe-upper end of the shell `of a plug. I

Figure 10 is a similar'view showing conventional welding apparatus inplan, as seen looking In the drawings, Figure 2 is a view showing alongitudinally grooved bar such as is used. in makingy insulatorsecuring members in accordance with the method wherein my inventionconsists. It may be made by a maker of spark plugs' by millingor'otherwise 4providing a longitudinally extending groove in each of thesix exposed faces of a hexagonal bar, such as is-shown in Figure 1;`

or such a ybar may be rolled or 'drawn at the rolling mill, or groovesmay be milled or other- ,wise provided in the exposed faces of suchahexagonal bar as is shown in Figure 1 before it is supplied tothemanufacturer oi' the plugs. A bar of the form shown in Figure 2 havinglongitudinally extendinggrooves I0 having been provided, a centralportion thereof of a diameter suiiiclently large to eliminate thebottoms of the groovesis removed from one end of the bar, see

' VFigure 3, which step provides attaching lugs Il spacedI apart fromone another andthe lower ends of which are adapted to'be welded to theupper end of a spark plug shell or casing l1. Figure 3 shows how thestep of' removing` the central portion of'relatively large diameter fromthe end of the b ar eliminates the bottoms of the groovesand' providesthe spaced apart attaching lugs. A`- second central portion of smallerdiame eter 'than and disposed beyondthe portion re. moved -tol providethe lugs. l I,' is also removed from the end 4,of the bar to thereby`provide an inwardly extending annular ledge I2'. through which theinsulating member Il of the plug extends; and the insulator lsecuringmember thus produced is cut'onfrom the end of the bar by showing how aspark plug havin'g radio shielding features may vention.

' Figure il is a view be made in accordance with my in illustrati'ng analternative the chuck of a machine tool of the turret lathe type, andfeeding 'a toolof the drill type into. the

f step which maybe madel use of in 'performingf the method ,wherein my'invention consists. Figure 9 is .a vie'w showing conventional weld- 55 atransversely movable tool I4. The upper end vention, of` the insulatorsecuring memberis commonly Figure 6 ,is a view showing' a section upon.la 45 chamfered, -asshown at I B.- which may be done .transverse planeindicated by the lines-l, Fig' .by an inclined cutting edge upon thetool il ure 5. or by a separate and distinct instrument or deend of thebar; and the smaller portion vwhich 'lies beyond saldlarger portionand-provides the ledge I2 is 'preferablyv produced in the same way ,bythe.

by a tool of smaller diameter,` which may be either an extension of thelarger tool which removes the bottoms of the grooves or a separate anddistinct tool. As an alternative procedure the insulator securingmemberwith attaching lugs provided as hereinbefore explained, may be cut fromthe end of the bar before an inwardly extending ledge like the ledge I2is provided, thus leaving said member with an imperforate'end wall IB,as shown in Figure 8, the central portion of which will be removed bydrilling or otherwise to provide an inwardly extending annular ledgewhich surrounds the insulating member in the finished plug. l

In makinga complete spark plug an insulator securing member made inaccordance with my improved method andhaving the features ofconstruction and operation hereinbefore enumerated is assembled with ashell or casing I1 having a lower threaded portion adapted to screw intoa threaded opening in aninternal combustion engine cylinder; aninsulating Vmember I3 vherelnbefore referred to; and suitable YgasketsI8,

I9 as shown in Figures 4 and 5; except that when first'assembled thelower ends of the lugs II are provided with a lining 28 of insulatingmaterial;

and `it is commonly made in a turret lathe by the not yet welded to theupper end of the casing I1. The assembly thus formed is then placedbetween pressure applyingmembers 20, 2I of a suitable press, asindicated conventionally in Figure 9; and pressure applied by the presscompresses the gaskets I8, I9 sufficiently to secure gas tightness intheplug. While pressure is a maintained vand the gaskets are held undercoml pression the lower ends of the lugs II are electrically welded'to`the upper end of the shell I1 by current supplied through electrodes 22adapted to engage the lower ends of the lugs I I.

Six electrodes are used so that plug does not have to be rotated tobring the lugs into line with the electrodes; and oppositely disposedpairs of them are operated in unison as appears in Figure 10 to pressthe lower ends of the lugs II against the periphery of the shell whilethe weld- ',ing is being done, by iluid operated pistons withincylinders 23, one associated with each electrode.

Any suitable welding apparatus may, however, be used in making a sparkplug in accordance with my invention; and the showing of such a suitablewelding apparatus is intended tobe and is in fact conver tional only.

The circumferentially extending bead 24 at the upr .r end of the casingI1 is tolocalize the heating during the welding of the lower ends of thelugs II to the shell; and the at faces 25 provided by chamfering thevangles of the hexagonal bar are for securing enlarged areas of contactand better bearings between the lugs I I and the welding electrodes 22.

Figure 7 shows an insulator securing member same general method stepsemployed in making an insulator securing member of the form rst hereindescribed. This radio shielding form of my invention is assembled withand secured to the'casing of the plug by welding the lugs II thereto, ashereinbefore explained, and by apparatus such as is shown conventionallyin Figures 9 and 10; the upper pressure applying member 2| beingmodified so as to receive the shield tube 28 as will be understood.

Having thus described and explained my invention I claim and desire tosecure by Letters Patent:

l. The method of making an insulator securing member for a spark plugwhich consists in providing a hexagonal bar having a longitudinallyextending groove in each of its six exposed faces; removing a centralportion of a diameter such that the bottoms of said grooves are cut awayduring such removing step from one end of said bar, to thereby provide aseries of separate and independent attaching lugs spaced apart from oneanother; removinga second central portion continuous with and of lesserdiameter than said first portion from said bar to thereby provide aninwardly extending annular ledge located beyond said attaching lugs; andsevering the part thus formed from said bar beyond said' inwardlyextending ledge.

2. The method of making a spark plug which consists in making aninsulator securing` member in accordance with the method defined inclaim l; assembling said insulator securing member with an insulator andwith a spark plug shell;

and welding the extremities of said lugs to the bar, thereby providing aseries of separate and independent attaching lugs spaced apart from oneanother. f

HECTOR RABEZZANA.

